The present disclosure relates to a laser scanning unit including a deflector which reflects a light beam emitted from a light source while oscillating about an oscillation axis, to perform deflection/scanning, and an image forming apparatus including the same.
Conventionally, some laser scanning units used in a laser printer, a copying machine, or the like use a Micro Electro Mechanical Systems (MEMS) mirror as a deflector which deflects a laser light beam emitted from a light source, to scan the circumferential surface of a photosensitive drum. The MEMS mirror has an oscillation axis perpendicular to a normal direction of the mirror, and is driven so as to oscillate about the oscillation axis in a reciprocating manner, thereby performing scanning in a predetermined scanning range on the photosensitive drum with the laser light beam.
A general MEMS mirror is oscillated sinusoidally. Thus, a scanning speed is the lowest at the end portions of the scanning range, and is the highest at the center portion of the scanning range. Due to this, a problem arises that the beam diameter of the laser light beam does not become uniform over all image heights in the scanning range. In order to realize uniform-speed scanning with a MEMS mirror which oscillates sinusoidally, it is necessary to use an arc sine lens as a scanning lens. Meanwhile, in order to make the beam diameter uniform over all the image heights, it is necessary to use an fθ lens as a scanning lens. However, the use of the arc sine lens achieves uniform-speed scanning but does not achieve uniformity of the beam diameter, and the use of the fθ lens achieves uniformity of the beam diameter but does not achieve uniform-speed scanning. That is, both uniform-speed scanning and uniformity of the beam diameter are not achieved at the same time.
A conventional laser scanning unit uses an arc sine lens as a scanning lens and controls a light emission time period and a light amount of a laser light beam, thereby ensuring uniformity of the beam diameter. Another conventional laser scanning unit uses an fθ lens as a scanning lens and controls light emission timing and a light emission time period of a laser light beam, thereby obtaining an effect corresponding to uniform-speed scanning. However, in order to realize these types of control, emission timing control with high accuracy, light amount control in a very wide range, and the like are required, and thus a problem arises that an emission control circuit becomes large in scale and expensive.